A demand exists for fluorinating agents which are site-selective towards organic, especially carbanionic, substrates, especially for use in the preparation of pharmacologically active compounds. A number of such electrophilic fluorinating agents are known but, until recently had limited commercial utility because such agents were expensive, hazardous, inconvenient to handle, unstable and/or insufficiently selective for general use.
Ronald Eric Banks has disclosed in copending U.S. patent application Ser. No. 08/163,257, filed on Dec. 7, 1993 that N,N'-difluorinated diazoniabicycloalkane derivatives of the following Formula I are effective electrophilic fluorinating agents: ##STR2## wherein n represents 0, 1 or 2;
each R.sup.1, R.sup.2, R.sup.3, R.sup.4 and R.sup.5 independently represents hydrogen, C.sub.1 -C.sub.6 alkyl, aryl, C.sub.1 -C.sub.6 alkyl-substituted aryl or aryl-substituted C.sub.1 -C.sub.6 alkyl; and PA1 each X.sup.- represents a counterion or 2X.sup.- represents a single divalent counterion. PA1 Y represents a readily fluorinatable Lewis acid, PA1 and X corresponds to the counterion X.sup.- and, PA1 when the relevant compound is formed by fluorination of a Lewis acid adduct, X.sup.- is YF.sup.-. PA1 each R.sup.1, R.sup.2, R.sup.3, R.sup.4 and R.sup.5 independently represents hydrogen, PA1 C.sub.1 -C.sub.6 alkyl, aryl, C.sub.1 -C.sub.6 alkyl-substituted aryl or aryl-substituted C.sub.1 -C.sub.6 alkyl; and PA1 each X.sup.- represents a counterion or 2X.sup.- represents a single divalent counterion.
Various methods of preparing these compounds are described in the above-mentioned copending patent application. In terms of the 1,4-diazoniabicyclo[2.2.2]octane derivatives (n is 0, and each R.sub.1 is hydrogen), the relevant reaction sequences are represented as follows: ##STR3## wherein R' is a C.sub.1 -C.sub.6 alkyl group,
The remaining compounds of Formula I are prepared from analogous reactants.
1,4-Diazabicyclo[2.2.2]octane (otherwise tetra-ethylenediamine, TEDA) is commercially available under, for example, the Trade Mark DABCO (Air Products and Chemicals Inc.) for use in the manufacture of urethane foams, elastomers and coatings, epoxy resins, and the like articles. N,N-Tetrahalo-1,4-diazoniabicyclo[2.2.2]-octanes in which the halogen is chlorine, bromine or iodine are known and can readily be prepared from 1,4-diazabicyclo[2.2.2]octane by, for example, treatment with the halogen in carbon tetrachloride (see U.S. Pat. No. 2,964,526).
However, the corresponding tetrafluoro compound is unknown and cannot be prepared in an analogous manner. Attempts to fluorinate 1,4-diazabicyclo[2.2.2]octane with fluorine to produce 1,4-difluoro-1,4-diazoniabicyclo[2.2.2]octane difluoride gave an unidentified white solid which showed some fluorinating capacity but readily decomposed at ambient temperature into a coloured material having no electrophilic fluorinating power.